235/75R15 is 1.77" shorter than 265/75R15, a −5.78% change in diameter. That is more than the 3% many tire shops use as a limit, so plan on recalibrating the speedometer and checking ABS and stability control.
Ground clearance changes by 0.89" (half the diameter change), and the tire needs 0.89" less room above it.
265/75R15 is 1.18" wider. On the same wheel offset about half of that, 0.59", moves toward the suspension and half toward the fender.
Both fit a 15" wheel; the sidewall is 0.89" shorter on 235/75R15.
Details: 265/75R15 in inches · 235/75R15 in inches · change sizes in the calculator